It is well known that various heterogeneous catalysts may be used to hydroformylate various olefins. Most commercial heterogeneous catalysts, however, are poorly characterized materials which have a distribution of active sites which exhibit variability in their nature, activity, and selectivity.
Despite these drawbacks, there are often significant process advantages accrued when a heterogeneous catalyst is employed. Homogeneous catalysts, which offer uniform composition and reactivity, and often fewer by-products, can present difficulties in separating product from the catalyst (an especially important point if the catalyst is based on a precious metal such as rhodium) and may have increased energy requirements. The advantages of both modes of reaction would be offered if one would attach a homogeneous catalyst to an insoluble backbone, a process termed heterogenization.
Heterogenization of a homogeneously active catalyst is not a new idea; quite a bit of work has already been carried out on this concept, but the previous supports have most often consisted of chemically-modified inorganic and organic polymers. These materials suffer from low chemical and thermal stability (due to the reactivity of the support), have a variety of active sites (like a conventional heterogeneous catalyst) due to the geometric irregularity of the polymer, and often exhibit leaching of the catalyst into the product stream, affording a separation problem similar to that of homogeneous catalysts. The layered zirconium phosphonates and analogous compounds (especially the layered species) have been found to be suitable support materials for compositing with active hydroformylation catalysts comprising rhodium metal and salts and other compounds thereof. The layered structure of such zirconium phosphonates and analogous compounds provide uniform catalytic sites and may be chemically modified to minimize leaching. Furthermore, more demanding processing conditions could be encountered without degradation of the support. Finally, the two-dimensional geometry of the interlayer space may result in an enhanced selectivity towards entering reactants or product formation.